The present invention relates to the copper clad laminate for the film or the substrate that is used for the printed circuit, the multilayer printed circuit board, and their processing method. As described on P.299 to 564 of Purinto Kairo Gijutsu Binran (Printed Circuit Handbook, the 2nd version published by Nikkan Kogyo Shinbun Co. Ltd.), the copper clad laminates include; (1) the laminate made of copper foil and paper based phenolic resin, paper based epoxy resin, paper based polyester resin, glass cloth based epoxy resin, glass cloth based polyimide resin, glass cloth based bismaleimide-triazine resin or glass cloth based fluoroplastics, (2) the laminate made of copper foil and the aramid cloth impregnated with epoxy resin or low dielectric constant resin, and (3) composite copper clad laminate consisting of the glass cloth based epoxy resin layer, and paper or non-woven glass cloth based epoxy resin as core material. Said laminates are rigid copper clad laminates; in addition, there is available another type of copper clad laminate for flexible printed circuit board made of normally one sheet of thin flexible plastic film and the copper foil using the adhesive. Polyester film and polyimide film are used as the plastic film.
The copper foil can be classified into two types; the electrodeposited copper foil and the rolled copper foil. Furthermore, they can be classified into many types according to the classification method; e.g., classification of the copper foil corresponding to the resin to be used or classification according to the copper foil thickness and mechanical properties.
Adhesive coated cooper foil has been used for the phenolic resin copper clad laminate and the copper clad laminated for the flexible printed circuit board, hitherto. Furthermore, in the case of the epoxy resin copper clad laminate and the polyimide resin copper clad laminate, the resin material has been used as insulation layer to adhere the copper foil directly. In recent years, the conductor spacing of the printed circuit board has been considerably reduced due to the increased density and reduced weight and size of the electronic equipment. This trend has led to the requirements as inhibition of blisters when immersed in the molten solder bath, elimination of any problem in drilling operation and resistance to plating chemicals when plating is required. Such extremely severe properties, with smaller circuit configuration, have come to be required. These requirements, in turn, strongly require adhesion strength between the copper foil and such insulation layer such as synthetic resin substrate. In order to ensure adhesive strength, the copper foil adhesion surface is normally provided with fine particles (called roughing) on the convex part of the concave and convex structure of the electrodeposited copper foil called raw foil or base foil to ensure anchor effect of improving adhesive strength from the microscopic viewpoint in the case of electrodeposited copper foil; furthermore, it is provided with barrier forming and rust preventive treatment. This roughing treatment ensures adhesion strength between the copper foil surface and insulations layer to be maintained on the level of practical use. However, on the other hand, firstly in the circuit forming process, the concave and convex structure formed on the copper foil surface is not etched within a predetermined etching time to remain as residual copper on the substrate surface so that it becomes the cause of deteriorating the electric properties, and it requires a considerable etching time for removing this residual copper. This has caused the degree of side etching to be increased, making it difficult to form a fine circuit. For this purpose, low profiling is required in recent years, and the limit has been reached by trade off with adhesion strength. Secondly, since the concave and convex structure of the copper foil causes the high frequency waveform to be disturbed, further low profiling has been required.
Conventionally, epoxy resin and butyral-phenol resin based adhesives have been used as adhesives for copper foil and synthetic resin substrate (insulation substrate). Adhesion with copper foil is based on the hydrogen bonding and the anchor effect which uses the fine particles formed on the copper foil surface, and this was not direct chemical bonding; therefore, sufficient adhesion strength could be ensured only when shiny side (smooth surface) of the copper foil was provided with roughing treatment including black treatment.
As described above, in the laminates comprising the copper foil and insulation layer according to the prior art, adhesion strength has been increased by the anchor effect which is provided by fine particles attached on the protrusion of the base foil (raw foil) of the copper foil. As result, (1) in etching for circuit forming process, much time was required to remove the protrusion and fine particles embedded in the insulation layer (e.g. synthetic resin substrate), and side etching occurred to the copper foil; so reduction in the fine wiring width was limited, and the limit of fine wiring forming for copper foil has been considered to the limit the width of 0.1 mm in the industrial area. (2) Roughing by providing fine particles has led to increased number of processes and decreased yield; thus, it has been difficult to reduce copper foil production costs. (3) Roughing conditions has been difficult to control, making it difficult to ensure uniform product quality. (4) Furthermore, in order to ensure powerful adhesion between prepreg and copper foil, black treatment has been necessary to maintain adhesion strength between the copper foil shiny side in the formation of multiple layers of the multilayer circuit board.
On the other hand, adhesion between the rubber material and metal or between the rubber material and laminate is disclosed in the U.S. Pat. No. 4,446,198, Japanese Patent Laid-open NO. 51-57783, Japanese Patent Publication NO. 60-14836, Japanese Patent Publication NO. 56-19820, Japanese Patent Laid-open NO. 54-53180 and Japanese Patent Laid-open NO. 1-201454. There is no instance, however, where the metal layer is to provided on the copper foil, and adhesion through cross linking between the copper foil and insulation layer is provided by chemical bonding through sulfur atom. Furthermore, Japanese Patent Laid-open NO. 3-111464 describes the case of using the acrylonitrile rubber containing zinc oxide as adhesive between the laminate and copper foil, but does not refer to metal layer provided on the copper foil and adhesion through cross linking by chemical bonding through sulfur atom.